1. Field of the Invention
The present invention relates generally to fluid reaction surfaces, and more specifically to variable guide vanes in a turbomachine.
2. Description of the Related Art Including Information Disclosed Under 37 CFR 1.97 and 1.98
In a turbomachine such as a gas turbine engine, a compressor includes multiple stages of rotor blades to progressively compress air for use in the combustor to produce a hot gas flow that passes through a turbine to extract mechanical power. A turbofan engine includes a large fan assembly connected to the rotor and located in front of the first compressor blade. Turbofan engines are required to operate efficiently over a wide range of flight conditions and speeds. These conditions include maximum power takeoff and climb, part-power cruise, and low-altitude, low-power loiter. In order to meet these requirements of variable thrust while maintaining an acceptable level of specific fuel consumption, it is common to selectively vary certain flow areas and characteristics within the fan and core portion of the engine. One of the flows which may be varied is that in the fan duct, and this may be accomplished by use of variable inlet guide vanes (IGV's) which are selectively varied over a range to modulate the total airflow in the duct.
Large turbofan engines include variable inlet guide vanes having a complex mechanical connection and include seals, bushing, actuators and other mechanism to control the position of the guide vanes. These are very complex and costly, especially for use in small gas turbine engines.
An example of a complex inlet guide vane apparatus is shown in U.S. Pat. No. 5,215,434 issued to Greune et al on Jun. 1, 1993 entitled APPARATUS FOR THE ADJUSTMENT OF STATOR BLADES OF A GAS TURBINE. For a small turbofan engine, use of the arrangement would add a high cost to a rather low priced engine.
Guide vanes include a leading edge portion and a trailing edge portion. Some variable inlet guide vanes provide a fixed leading edge portion while the trailing edge portion pivots with respect to the leading edge portion. U.S. Pat. No. 4,741,665 issued to Hanser on May 3, 1988 entitled GUIDE VANE RING FOR TURBO-ENGINES, ESPECIALLY GAS TURBINES shows one of these.
Some inlet guide vanes include a fixed middle portion with the leading edge and trailing edge portions variable with respect to the fixed middle portion such that the entire length of the vane chord is variable. U.S. Pat. No. 3,295,827 issued to Chapman et al on Jan. 3, 1967 entitled VARIABLE CONFIGURATION BLADE shows this configuration. This type is also a complex arrangement and therefore would be costly for a small turbofan engine.
U.S. Pat. No. 4,029,433 issued to Penny et al on Jun. 14, 1977 entitled STATOR VANE ASSEMBLY shows a simple variable vane mechanism in which vanes are supported on a fixed wall at one end and on a movable sleeve on the other end, where the movable sleeve is displaced in an axial direction to vary the angle of the vanes. This arrangement is less complex than the others, yet it still includes an actuator and linkage to provide pivot movement of the vane.